Low water loss cement slurries comprising carboxymethyl dextran and salts thereof



United States Patent 2,902,378 Patented Sept. 1, 1959 1 2 The degree of substitution of the carboxymethyl ethers 2,902,378 obtained by reacting the sodium derivative with chlor- LOW WATER IJOSS CEMENT SLURRIEG COMPRIS- ncetic acid depends on the degree of substitution of the intermediate with respect to the alkali metal.

ggfifi DEXTRAN AND SALTS 5 It follows that the carboxymethyl group content of the dextran ether obtained by reacting the sodium dextran Harry A. Tonlmin, Jr., Dayton, Ohio, assignmto The produced by the non-aqueous alcoholic method with chlor- Commonwealth Engineering Company of Ohio, Dayacetic acid is also a maximum of 0.3 such groups per tel! Ohio gnhydroglucose unit. Those very low-substituted ethers 0 not have the combined properties of inhibiting de- No Drawmg' gzgiggg 1956 hydration of the slurry and permitting the cement, after placement thereof, to set in the normal time.

4 CllimS- The carboxymethyl dextran incorporated into aqueous cement slurries in the practice of this invention are ob- This invention relates to cement slurries and to a 15 ta n d y reacting the water-soluble, native, unhydrolyzed method of cementing. dextran with an alkali metal chloracetate, such as sodium One of the problems encountered in the cementing of or potassium chloracetate, in an aqueous solution conoil wells and in grouting cracks in masonry structures is wining an alkali metal hydroxide Such as Sodium 01 pcthe set-up time. Cement slurries are usually modified by tessium hydroxide. at 10 a time ythe inclusion of some material which retards dehydration 8 inversely with the temperature between two u s of the slurry so that the viscosity is not increased due to and about One waier 1 d can b il l d i i i The molar ratio of sodium or potassium chloracetate The materials used to retard the dehydration of the t0 is between 211 and 1211, the molar ra o of slurry have also prolonged the set-up time to an undesir- 505111111 Potassium hydroxide o dcXt an is between 5:1 able extent. Also, those materials tend to detract from and 15 and the molar ratio of water to dextran is bethe strength of the dried cement. tween 7011 12011- A primary obieci f this invention i to provide new The reaction product is a viscous solution of the alkali and improved cement slurries containing a new material metal salt, -8" the Sodium Potassium lt of the .which prevents dehydration of the slurry until it is in whoxymethyl dextrah in Water containing the eXeeSS place and at the same time does not delay the set-up time kah metal hdf0Xide and c loracetate. beyond the normal time required for setting of the cement. The atkah metal Salt 0f the eal'hexymethyl dextran c n This and other objects are accomplished by the present he used 111 the aqueous cement slurries, Particularly if the invention in accordance with which it is found that slurryhasapH the alkaline Sidespggific carboxymethyi ethers f ifi dextrans, unlike The free ether is isolated from the solution of the alkali starch and carboxymethyl starch, and in small amounts, lhetal Salt, by l hg the P f he Solution to the acid effectively inhibit the dehydration of cement slurries withslde F then precipitating the ether om t e acidified out deiaying the normal setting time f the cement Once solution by means of a water-miscible alcohol or ketone. i i place" This removes the electrolytes as NaCl. The ether can The carboxymethyl dextrans used for the present purbe pl'cclpttateft satisfactorily at P poses, and whicmnexpected combination f 40 The following example illustrates the production of a properties mentioned, are derived from water-soluble nacafboxymethyl F alkeh metal Salt nd f ee ether iimgh droiyzed dextrans and suitable for use in the present improved cement slurries. aLigLLwyp 19 fl mwhydrw One hundred parts of particulate purified native (unglucose unibof the dextram hydrolyzed) L.m. B-512 dextran were dissolved in 700 By wate'i-soluble native dextran is meant the dextran Parts watert hundred and y Parts of sodium produced by the action of certain bacterial strains on hydroxide were dissolved in 150 parts of water, and the sucrose under conventional conditions leading to the prodamn 5 f f hydmxide Solutions e xed toduction of dextran having a molecular weight estimated gather with agltatloh' TWO hundred and w n y parts to be in the millions and which is precipitated from the of monochloracetlc acid were dissolved in 400 parts of fermentate by means of a water miscible aliphatic alcohol water and 112-3 Parts of ahhydr 011$ Sodium nat or ketone, i h hydrolysis b f or ft such precip were added to the solution. The resulting chloracete itation. Water-soluble native dextrans from which the sohinon was F slowly added to the miXed n and carboxymethyl ethers may be derived are those bearing Sodium hydroxide solutions, and the mass was heated h f ll i N R (Northern Regional Research for one hour at 65 C. The reaction mass was then adoratories) designations: Leuconoszoc mesenteroides B- t0 PH with hydrochloric acid and P d slow- 114 1064 B 1414 1 45 512 10 1203 ly into 1500 parts Of methanol. The precipitate was Sub- B 1119, 134417 and so on stantially freed of methanol and water by passage through Th carboxymethyi ethers f these dun-ans have to be squeeze rolls, then dried under vacuum and reduced to prepared under particular conditions in order to assure Pamculate condition mesh) in a hammer l. The the sub tit i f a i i (average) f 0 carboxy final product contained, by analysis, an average of about methyl group per anhydmgiucose i f the dexmm Mi carboxymethyl group per anhydroglucopyranosidic Unlike the carboxymethyl ethers of starch, cellulose and dextrin, the dextran ethers having the desired minimum Ethel's htaihh1g an average of more n 1-0 and up content of carboxymethyl groups cannot be Obtained by to 3.0 carboxymethyl groups per anhydroglucopyranosidic methods involving the production of an intermediate 211- mm are obtained under the Same general ditions exkali metal-substituted dextran in a non-aqueous, alcoholic *P that the amounts 05 sodium or Potassium ydroxide, medium, and than reacting the intermediate with chief. and of sodium or potassium chloracetate, may be inacetic a id, o l very small amounts f Sodium are creased as noted above, and/or the reaction time may troduced into the dextran in non-aqueous alcoholic mebe extended and may be p to about t o ou Other dium. The maximum obtainable sodium. content of the being equal, an increase n the reaction temdextran produc so produced is an average of 0.3 sodium Pereture also t introduction f mo e carper anhydroglucese unit of the dextran.

boxymethyl groups into the dextran molecule.

Very small amounts of these carboxymethyl dextrans or alkali metal salts, i.e., from 0.01% to 0.1%, are effective to retard the dehydration of the cement slurry without delaying the setting time. Tests show that the slurry is readily pumpable and retains the required fluidity for proper placement thereof for a practical period of time and that the cement, after being placed, sets up in substantially the same time as if the dextran ether or ether salt were not present. This is in contrast to slurries modified by inclusion of other conventional water-loss retardants, such as starch and earboxymethyl starch, which prolong the setting time for as long as 30 minutes and even longer. The carboxymethyl dextran or alkali metal salt does not detract from the strength of the set cement, as do the conventional water-loss retardants but tends to enhance it, which latter eflect can be attributed to the extremely high molecular weight (in the millions) of the parent dextran and the fact that, with a minimum average of 1.0 carboxymethyl group per each of the extremely large number of anhydroglucose units making up the dextran molecule, the overall content of carboxymethyl groups is very high.

The slurries of the invention may be made up by mixing the dry ingredients comprising hydraulic cement and carboxymethyl dextran or salt together with, optionally, inert filler material such as sand or crushed limestone. Such mixtures can be prepared in advance and then mixed with water prior to use. Also, the various ingredients can be mixed with water separately and then combined to form the cement slurry, provided that the hydraulic cement is mixed with water immediately before the slurry is used.

The term hydraulic cement is intended to include all mixtures which are commonly known as hydraulic cement. This includes mixtures 'of lime, silica and alumina, or of lime and magnesia, silica and alumina and iron oxide (magnesia, for instance, may replace part of the lime, and iron oxide a part of the alumina). Hydraulic cements include hydraulic limes, grappier cements, pouuolanic cements, natural cements and Portland cements. Pozzuolanic cements include slag cements made from slaked lime and granulated blast furnace slag. Portland cement is a preferred hydraulic cement because of its superior strength.

The carboxymethyl dextran or alkali metal salt is also eifective in retarding dehydration, without increase in setting time, of those aqueous cement slurries which are modified by the inclusion of inert granular fillers such as sand, ground limestone, or the like.

The water used with the dry ingredients to make the slurry is just suflicient to render the slurry fluid and easily pumpable.

As an example of the practice of the invention, the following is given:

A Portland cement slurry is made up with fifteen pounds of cement to the gallon of slurry, and there is added to it about 0.05% of carboxymethyl dextran derived from L.m. B-512 native, unhydrolyzed dextran and containing an average of 1.0 carboxymethyl group per anhydroglucose unit. and does not dry out on standing, is readily pumpable and sets promptly when placed. In comparison, a similar Portland cement slurry was prepared, but without The slurry, which remains fluid the inclusion of the carboxymethyl dextran. If the slurry were placed immediately and the amount used was small, as in a minor grouting operation, the slurry could be placed and set in the normal time, but the slurry could not be allowed to stand for even a short period without some drying out which made it more diflicult to pump. A similar Portland cement slurry was prepared containing 0.05 of carboxymethyl starch. The slurry remained pumpable for a longer time than the neat" slurry, but setting thereof was delayed for some 20-30 minutes.

It will be understood that the example given is for purposes of illustration and that some changes and modiflcations may be made in details in practicing the invention. Since such changes may be made without departing from the spirit and scope of the invention, it is intended to comprehend them in the appended claims.

This application is a continuation-impart of application Serial No. 440,850, filed July 1, 1954, and now abandoned.

What isclaimed is:

1. A fluid, pumpable, hydraulic cement slurry consisting essentially of a hydraulic cement, an amount of water sufiicient to render the slurry initially fluid and pumpable and, for maintaining the initial fluidity and pumpability of the slurry prior to placement without delaying the setting time for the cement after placement of the slurry, from about 0.01% to about 0.1% of a substance selected from the group consisting of carboxymethyl ethers of native, water-soluble, unhydrolyzed dextrans containing an average of from 1.0 up to 3.0 carboxymethyl groups per anhydroglucose unit, and alkali metal salts of said ethers.

2. A fluid, pumpable, hydraulic cement slurry as in claim 1, characterized in containing from about 0.01% to about 0.1% of a carboxymethyl ether of a native, water-soluble, unhydrolyzed dextran containing an average of from 1.0 up to 3.0 carboxymethyl groups per anhydroglucose unit.

3. A fluid, pumpable, hydraulic cement slurry as in claim 1, characterized in containing from about 0.01% to about 0.1% of an alkali metal salt of a carboxymethyl ether of a native, water-soluble, unhydrolyzed dextran containing an average of from 1.0 up to 3.0 carboxymethyl groups per anhydroglucose unit.

4. In the making of an aqueous hydraulic cement slurry consisting essentially of the cement and sutficient water to produce an initially fluid and pumpable slurry, the improvement which comprises prolonging the fluid, pumpable condition of the slurry prior to placement thereof, without delaying the setting time for the cement after placement of the slurry or decreasing the strength of the set cement, by including in the slurry a small amount of a substance selected from the group consisting of carboxmethyl ethers of native, unhydrolyzed, watersoluble dextrans containing an average of from 1.0 up to 3.0 carboxymethyl groups per anhydroglucose units.

References Cited in the file of this patent UNITED STATES PATENTS 2,360,327 Bailey et a1 Oct. 17, 1944 2,562,148 Lea July 24, 1951 2,673,810 Ludwig Mar. 30, 1954 

1. A FLUID, PUMPABLE, HYDRAULIC CEMENT SLURRY CONSISTING ESSENTIALLY OF A HYDRAULIC CEMENT, AN AMOUNT OF WATER SUFFICIENT TO RENDER THE SLURRY FLUID AND PUMPABLE AND, FOR MAINTAINING THE INITIAL FLUIDITY AND PUMPABILITY OF THE SLURRY PRIOR TO PLACEMENT WITHOUT DELAYING THE SETTING TIME FOR THE CEMENT AFTER PLACEMENT OF THE SLURRY, FROM ABOUT 0.01% TO ABOUT 0.1% OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF CARBOXYMETHYL ETHERS OF NATIVE, WATER-SOLUBLE, UNHYDROLYZED DEXTRANS CONTAINIGN AN AVERAGE OF FROM 1.0 UP TO 3.0 CARBOXYMETHYL GROUPS PER ANHYDROGLUCOSE UNIT, AND ALKALI METAL SALTS OF SAID ETHERS. 